How to buff weaker class/ subclass player wants to play without making it too strong

So I’ve been thinking about allowing players who want to play weaker classes (like rogue) small buffs to make them feel better. For example I was thinking of giving a player who wanted to use Scion of three the ability to regain 1 charge of bloodlust if they killed the target. Would that be too strong? I also considered moving the level 13 feat to level 9 and level 17 feature to level 13 as they both (and especially the level 13 feature) feel very weak but idk.

How do you guys handle players asking for small/ medium buffs to their class, especially when it’s a weaker class?